The Early Manifest Glaucoma Trial is intended to study whether and to what extent current standard therapy, reduction of the intraocular pressure, influences the course of chronic open angle glaucoma. It is a prospective, randomized study in which two groups of patients, one treated with laser trabeculoplasty and betaxolol and the other untreated, are closely followed with computerized perimetry and fundus photography. The project has been reviewed and approved by the Swedish Medical Research Council (051192) and by the Ethics Committee of the Medical Faculty of the University of Lund (061592). Funding has been obtained for an open study on 200 participants to be carried out at the Department of Ophthalmology at the General Hospital of Malmo, Sweden. Preliminary studies of screening methods begun in 1991. Recruitment for the trial started October 5 1992. The present application is requesting support for a number of modifications intended to strengthen the original study plan. They include: - a major increase in the number of participants (from 200 to over 300). This would improve the power of the study to detect a limited but clinically meaningful effect (from approximately 70 to 90 per cent) at the cost of a greatly expanded community screening effort. - the incorporation of a masking protocol intended to minimize potential sources of bias - the employment of a clinic coordinator - the establishment of an independent disc reading center - the participation of an independent data center with responsibilities described in a separate application. - the participation of an independent data and safety monitoring committee. It is expected, that the large scale community screening effort to recruit study participants with as yet undetected glaucoma, will require screening of 20,000 to 30,000 Malmo citizens in appropriate age groups.